A volute compressor is mainly composed of a fixed volute member and an orbiting volute member, which engage each other to form simultaneously several closed spaces having a volume which becomes gradually smaller toward the center from the outer edge. The working principle of the conventional volute compressor is illustrated in FIG. 1. An orbiting volute member 10 is caused to revolve in relation to a fixed volute member 11 so as to cause the working fluid 60 outside the two volute members, as shown in FIG. 5, to enter the closed spaces via an inlet 15 to bring about compression. The working fluid 61 in the closed spaces is then forced to exit via an outlet 16 adjacent to the center of the fixed volute member 11 by the continuous orbiting motion of the orbiting volute member 10. As the closed spaces become gradually smaller, the compression process of the working fluid is thus attained. The compressed high-pressure fluid is designated by a reference numeral of 63.
The working fluid in motion is compressed such that the compressed fluid generates in the closed spaces an axial resultant thrust Fa, a radial resultant thrust Fr and a tangential resultant thrust Ft, as shown in FIG. 2. The axial resultant thrust forces the two volute members to move apart axially while the radial resultant thrust and the tangential resultant thrust act on the volute members such that an overturn moment of force is generated to result in the overturn of the volute member capable of making an axial movement. It is therefore conceivable that these three resultant forces must be effectively overcome so as to prevent the compressed working fluid from leaking severely from the end surface 45 of the two volute members and from the side surface 47 of the volute piece. The severe leak of the compressed working fluid can bring about a tremendous reduction in volumetric efficiency of the compressor.
The prior art methods of overcoming the problem of leakage of the working fluid, which takes place in the end surfaces of the two volute members, are described respectively hereinafter.
As disclosed in the U.S. Pat. No. 4,365,941, the working fluid in the intermediate compression chamber is guided to arrive in the back pressure chamber located behind the orbiting volute member and formed by the skeleton and the fixed volute member. The motion of the orbiting volute member is thus brought about by a fluid back pressure generated in the back pressure chamber, thereby forcing the orbiting volute member to move to remain in a close contact with the fixed volute member so as to seal off the end surfaces of the two volute members.
Another U.S. Pat. No. 4,877,382 discloses a method in which the working fluid in the intermediate compression chamber or the high compression chamber is guided to enter the back of the fixed volute member. The fixed volute member is forced to move to remain in a close contact with the orbiting volute member by a fluid back pressure generated in the back pressure chamber formed by the sealing member and the circular groove located in the back of the fixed volute member, thereby effecting the sealing of the end surfaces of the two volute members.
Such prior art methods as described are limited in design in that the back of the volute member is directly acted on by the back pressure which is in fact the fluid pressure of the compressed working fluid. The axial resultant thrust Fa generated in the compression chamber can be therefore overcome; nevertheless the axial back pressure that is required to overcome the overturn moment of force M produced by the overturn fulcrum I must be greatly increased. This is due to the fact that the anti-overturn arm of force of the anti-overturn fulcrum J of the net axial force (back pressure resultant force Fb-axial resultant force Fa) acting on the volute member is shorter, as shown in FIG. 3. The excessiveness of the axial back pressure can bring about an excessive abrasion of the end surfaces of the two volute members, thereby resulting in a reduction in the mechanical efficiency of the compressor as well as an increase in the temperature of the compressor.
There is still another prior art method of overcoming the leakage problem of the working fluid, as disclosed in the U.S. Pat. No. 4,740,143. This prior art method makes use of elastic sealing members, which are disposed on the end surfaces of the two volute members. The elastic sealing members 91 are precision components which can not be made econmically. In addition, the use of such elastic sealing members as described above does not eliminate the route of the leak of the working fluid, as illustrated in FIG. 4.